Inkjet printing systems are in common use today. In one common form for swath printing, the printing systems includes one or more print cartridges mounted on a scanning carriage for movement along a swath axis over a print medium at a print zone. The print medium is incrementally advanced through the print zone during a print job.
There are various print cartridge configurations. One configuration is that of a disposable print cartridge, typically including a self-contained ink or fluid reservoir and a printhead. Once the fluid reservoir is depleted, the print cartridge is replaced with a fresh cartridge. Another configuration is that of a permanent or semi-permanent print cartridge, wherein an internal fluid reservoir is intermittently or continuously refilled with fluid supplied from an auxiliary fluid supply. The auxiliary supply can be mounted on the carriage with the print cartridge, or mounted off the carriage in what is commonly referred to as an xe2x80x9coff-axisxe2x80x9d or xe2x80x9coff-carriagexe2x80x9d system.
It is standard procedure to ship ink jet print cartridges xe2x80x9cwet,xe2x80x9d meaning full of ink. Ink exposure over time can compromise the structural and electrical integrity of the print cartridges. Print cartridges may spend a significant time in the shipping channels or on a merchandiser""s shelf before it is purchased. During this time, the print cartridges are constantly under chemical attack. In some cases, this attack could result in a print cartridge that is not operative when the customer installs it in their printer. This problem is compounded even further in systems that allow the customer to replace the ink supply without replacing the printhead. The desired printhead life in this type of system is 3 to 5 years, which includes a shelf life up to 18 months. If print cartridges could be shipped xe2x80x9cdry,xe2x80x9d the shelf life would increase and the ink exposure would not start until the print cartridge is purchased and put in use. This would require a printer that can prime the standpipe and nozzles after installation.
Air accumulation and excessive heating of the printhead can also result in a shorter life for print cartridges. The printing systems do not have the means of dealing with these problems actively. Instead air is warehoused inside the print cartridge, which in the absence of any other failure mode will eventually result in printhead starvation, and heat is dealt with by slowing the printer down when temperatures reach unacceptable levels.
Another problem that can lower the reliability of printing systems is excessive idle time. One problem associated with idle time occurs when large particles within the pigmented inks settle on the backside of the printhead and block ink flow. A second problem associated with idle time is water loss. If the ink loses enough water during idle times, sludge can develop in the print cartridge and lead to failure. The ink will sludge faster if it sits in a small ink channel, separated from a larger reservoir.
Standpipe particles can produce print quality failures during assembly, which ultimately increases the cost of manufacturing. A flushing routine can be used in an attempt to remove particles from the standpipe prior to attaching the printhead. This approach is not 100% effective.
Embodiments of this invention provide several reliability features that employ a recirculation path within a print cartridge, wherein fluid is recirculated within the print cartridge. One reliability feature is provided by active heat management, wherein the recirculation path is employed to provide printhead cooling. Another feature that can be provided is a self-priming print cartridge. Idle time tolerance can also be improved, with the ability to re-circulate ink and purge air, to provide a mode of operation that can improve the reliability of the print cartridge during idle times. A xe2x80x9ccleaning fluidxe2x80x9d can be introduced that could breakup the sludge as it circulates through the print cartridge. After several circulation cycles, the fluid is xe2x80x9cspitxe2x80x9d into a service station or printed onto paper. A further reliability improvement is provided through improved particle filtering. Each time a fluid is re-circulated through the system, it passes through the standpipe or plenum area and across the backside of the printhead. As the fluid moves through this region, particles that are trapped in the standpipe get swept out of the area and into a common chamber. From here, the fluid passes through a filter before it reaches the printhead again and any particles within the system are filtered out.